W. M. Wheeler.
The Temporary Social Parasitism of Lasius subumbratus Viereck.
Psyche 24(6):167-176, 1917.

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PSYCHE
VOL. XXIV DECEMBER, 191 7 No. 6
THE TEMPORARY SOCIAL PARASITISM OF LASIUS SUBUA$BRATUS V1ERECK.l ,
During the past summer, while studying the ants of the Sacra- mento Mountains, at Cloudcroft, N. M. (ah. 9,000 ft.), I had an opportunity to observe the method of colony formation employed by Lasius (Formicind) umbratus Nyl. subsp. suburnbratus Viereck. L. umbratus has long been known as a circumpolar species compris- ing several races, or subspecies and varieties, the names and known geographical distribution of which are recorded in the following list :
PALEARCTIC FORMS.
L. urnbratus subsp. urnbratus Nyl.
1
Northern and Alpine Eu-
subsp. rnixtus Nyl. rasia from Britain to. var. mixto-umbratus Fore1 Japan.
var. umbrato-affinis Ruzsky Russia.
subsp. rnixtus var. aphidicola Walsh Canada, Central and At- lantic States.
subsp. suburnbratus Viereck
British America, Rocky
Mts.
subsp. speculiventris Emery Known only from New Jersey.
subsp. vestitus Wheeler Known only from Idaho. subsp. minutus Emery Central and Atlantic States.
In Europe, according to Wasmann and Donisthorpe, the var. &to-urnbratus is more common than the typical urnbratus or mixtus, between which it is intermediate in size, color and pilosity. In the Eastern United States aphidicola is certainly the most 1 Contributions from the Entomological Laboratory of the Bussey Institution, Harvard University. No. 136.




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168 Psyche [December
abundant form of urnbratus. The subspecies speculiventris and vestitus are imperfectly known, the latter from a single female specimen, the former only from the types taken many years ago by Pergande at Caldwell, N. J. The subspecies rninutus is very sporadic. During the past eight years I have found only a single colony of it in the vicinity of Boston. The types of the sub- species suburnbratus were taken by Professor Cockerell at Beulah, N. M. (alt. 8,000 ft.). I have taken it at Williams, and on Mt. Lemmon in the Santa Catalina Range (9,000 ft.), Ariz., at Cloud- croft, N. M. (9,000 ft.), Lake Tahoe, Calif. (8,000 ft.), near Ottawa, Ontario, and Hull, Quebec and have seen specimens from Digby and Bedford, Nova Scotia. It is therefore the most boreal and steno- thermal of all the North American subspecies of umbratus and, as I have stated in a former paper (1917), properly belongs to the Canadian zone.
To the ethologist urnbratus is of unusual interest, because in Europe it is a temporary parasite of L. niger and in turn serves as the host of L. (Dendrolasius) fuliginosus, which is therefore a true temporary social hyperparasite. The young urnbratus queen is adopted by a colony of niger workers, which bring up her brood. Eventually these workers die off, probably in the course of four or five years, and the urnbratus colony, now pure, becomes very populous. Then it may in turn adopt a queen of fuliginosus, the offspring of which eventually supplant the urnbratus colony. In both cases the host queens are eliminated, probably by being assassinated either by their own workers or by the parasitic queens. The various phases in the development of the urnbratus and fuliginosus colonies have been studied by European myrme- cologists. The occasional occurrence of mixed colonies of um- bratus and niger and urnbratus and fuliginosus was noted by Schenck, Adierz, Forel, Wasmann and de Lannoy, but Emery and Forel in 1908 first suggested that they might be interpreted as arising from temporary social parasitism. Later Crawley and Donisthorpe fully demonstrated the truth of this conjecture by showing that the typical urnbratus is parasitic on the typical niger, the subspecies rnixtus on the subspecies alienus, and that urnbratus regularly functions as the temporary host of fuliginosus. Although North America is so rich in umbratus forms, no one has hitherto been able to prove from observations in the field that any



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19171 Wheeler-Social Parasitism of Lasius suburnbratus Viereck 169 of them is parasitic on some one of our varieties of L. niger. I
have repeatedly found dealated queens of aphidicola in small cavities under stones as if in the act of founding colonies inde- pendently in the same manner as most ants, but never with brood. Nor have I ever been able to find a mixed colony of L. niger var. americanus and aphidicola, even in Illinois where both forms are common in the same localities. The only indication that any American form of urnbratus may be a social parasite is furnished by some specimens of suburnbratus collected by Mr. W. Reiff in Nova Scotia and some experiments by Tanquary on minutus. At Bedford, near Halifax, Mr. Reiff took six dealated subumbratus queens from three colonies of what I recorded at the time (1910) as "the large yellowish form of Lash niger var. neoniger Emery." Since the discovery of Pergande's types of Alaskan ants I can now state definitely that this variety is sitkaesis. As Reiff's speci- mens were not accompanied by notes, the parasitism of subum- bratus could only be conjectured. Tanquary introduced succes- sively some eighty-eight of the small, active queens of minutus into twenty different colonies of L. americanus, nearcticus, brevicornis, claviger and interjectus-and obtained one case of adoption. This was in a colony of eight workers and a large number of cocoons of americanus. He concludes that "although one adoption out of 88 attempts is a small percentage, yet I think the ease with which this queen was adopted is very suggestive, and taken together with the facts mentioned above, namely the sporadic occurrence of the species, the very large number of females produced, the small size of the females, the fact that these females have not been seen in the act of founding a colony and one additional fact that may be mentioned, the mimetic coloration of the females (the color of these females is exactly the same as that of the darker form of americanus), I think justifies us in concluding that the queen of this species is in all probability, temporarily, parasitic upon the common L. americanus. "
My observations at Cloudcroft leave no doubt concerning the of the subspecies suburnbratus on two forms of L. niger, the var. sitka2nsis Pergande and the var. neoniger Emery. The former, as I have recently shown (1917), is the common form of niger at higher altitudes and latitudes from Alaska to Maine and Nova Scotia and southward along the ranges of the Sierra Nevada



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170 Psyche [December
and Rocky Mountains. The worker and female of this variety are large, brown or yellowish brown, with numerous erect or suberect hairs on the legs and antenna1 scapes. It passes over into the var. neoniger, which is smaller and darker, but has hairy legs and scapes, unlike our common and more xerothermic var. americanus, which closely resembles the European alienus in having the legs and scapes merely finely pubescent. At Cloudcroft sitkaensis is everywhere abundant in the pine forests at an altitude of 9,000 to 9,500 feet, and nests by preference under large stones. The females and workers have a peculiar and rather agreeable aroma, which is much stronger than that of americanus and much like the odor of subumbratus. On rocky slopes, exposed to the sun, especially along the edges of the alpine meadows, the typical sitkaensis is replaced by neoniger and forms intermediate in size and coloration. At altitudes of 7,000 to 7,500 feet or at higher elevations in very warm, dry situations the var. arnericanus and forms transitional to neoniger are not uncommon. At Cloudcroft I failed to find suburnbratus below 9,000 feet. Its colonies are very populous and live under large stones, usually in the shade of the pines. Its habits, like those of the other subspecies of urnbratus, are decidedly hypogseic. It does not make carton like the Euro- pean urnbratus. This is generally true also of our eastern aphidi- cola. I have, however, found a few colonies of this ant at Cole- brook, Conn., and Ottawa, Ontario, nesting in dark brown carton nests in the centers of rotten logs.
The observations proving that the young queens of suburnbratus establish their colonies with the aid of sitkahsis and neoniger workers may now be transcribed from my note-book: July 3 and 5. Four colonies of subumbratus were found under large stones.
Two were of considerable size and the superficial chambers of the nests were full of black males and golden yellow females ready for the marriage flight.
July 8.
The marriage flight of subumbratus must have occurred on July 6 or 7 as there were numerous dealated females running about among the stones on an open, sunny slope where many of the stones covered nests of neoniger. My son Ralph assisted me in carefully turning over the stones and examining these nests. In one area, about 200 feet in diameter, nearly every nest had from one to five dealated subumbratus queens running about in the large



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19171 Wheeler-Social Parasitism of Lasius subumbratus Viereck - 171 shallow superficial chambers.
By shading the chambers, which
were occupied by numerous neoniger workers and cocoons, the be- havior of the yellow queens could be readily studied. They ran in and out of the chambers and galleries leading into the soil and, when accosted by the neoniger workers, made peculiar supplicatory movements with the antennae, precisely like those of Formica consocians queens seeking adoption in nests of F. incerta. The neoniger workers, however, resented the intrusion and frequently seized the legs and antennae of the queens, though they soon re- leased their hold. The queens thus liberated often escaped from the nest and hid under stones near it or even in unfrequented nooks in the superficial chambers of the nest itself. On several occasions we saw a queen seize a neoniger worker, carry it out of the nest and release it uninjured. One queen was seen to snatch up a worker cocoon, carry it out of the nest and conceal it under an adjacent pebble. This is very suggestive of the behavior of the young Formica sanguinea queen that has entered a nest of F. fusca, but though it undeniably shows an interest on the part of the suburn- bratus queen in the neoniger brood, her method of colony formation is not that of F. sanguinea, for we soon discovered a depauperate neoniqer colony which had undoubtedly adopted a suburnbratus queen. The latter was moving to and fro very slowly and amicably in the midst of several neoniqer workers and their cocoons in a small recess under a stone. The ants were watched for some time and behaved precisely like members of a single colony. That the queens are nevertheless occasionally treated much more severely by the neoniqer workers, is apparent from the fact that we found a few recently killed and one partially eaten in the superficial cham- bers of some of the nests.
July 9.
Visited another rocky slope and an adjoining pine forest about a mile east of Cloudcroft and two miles from the lo- cality of yesterday's observations. Under the stones covering neoniger and sitkahsis nests there were many dealated subum- bratus queens eagerly seeking adoption. The following three colonies showed clearly that some of the queens had been or were being accepted :
1. A populous sitkaensis colony under several large contiguous stones among the pines. The superficial galleries of the nest were filled with workers and worker, male and female cocoons nearly



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172 Psyche [December
ready to hatch.
Under two of the stones a couple of subumbratus queens was found, each lurking quietly in a little cavity at the edge of a mass of cocoons nearly filling a large, shallow superficial cham- ber.
2. A similar but even larger sitkahis nest, also under a pile of stones, under three of which subumbratus queens were found. One of the queens was in a small cavity at the edge of a heap of co- coons while each of the others was resting on the very center of a collection of cocoons nearly as large as my palm. These queens had certainly been adopted and the picture presented was precisely like that of the recently adopted Formica consocians queens mounted on the cocoons and surrounded and fondled by the work- ers of F. incerta (Wheeler 1906). When the nest was disturbed the queens hurried into the galleries and disappeared in the soil. . They had evidently become strongly negatively heliotactic, unlike queens that are still running about on the soil immediately after the marriage flight.
3. A fine sitkdnsis nest under a single large stone among the pines had an adopted subumbratus queen surrounded by dozens of workers in the center of a pile of worker and female cocoons nearly as large as my hand. She quickly slipped into a burrow and was only recovered by digging down into the soil to a depth of more than six inches. In this nest a few of the female sitkaensis pup= were naked, i. e., not enclosed in cocoons.
Further search in the same locality brought to light two mixed colonies consisting of subumbratus and sitkaensis workers. I failed to find the queens of the former species, which were probably pres- ent but hiding deep in the soil. The failure to find them is not surprising as one very rarely secures the mother queen of a fully developed colony of any of our species of Lasius without extensive and very careful excavation of the nest. The foregoing observations show that the subumbratus queen has to acquire the brood odor of the host before she can be accepted. She therefore lurks very near the cocoons in a small earthen cavity and somewhat later, in the early stage of adoption, like Formica consocians, takes up a position on the brood. This renders her immune to attack by the host workers and gradually accustoms them to her presence. That adoption can be secured in very populous and flourishing colonies of sitka2nsis is shown by the



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19171 Wheeler-Social Parasitism of Lasius subumbratus Vzereck 173 observations of July 9. Nevertheless these observations throw no light on three interesting problems, which may be briefly consid- ered :
1. The first problem relates to the elimination of the host queen, evidently a conditio sine qua non of successful colony formation by such temporary social parasites as suburnbratus. The elimination is supposed to be effected in one of three ways: Either adoption succeeds only in host colonies that have already lost their rightful queen through death by accident or old age, or the queen is killed by her own workers after and because the young parasitic queen. has secured their allegiance, or the latter assassinates the host queen. The first hypothesis seems to be supported by the above described adoption of a subumbratus queen in a depauperate colony of neoniger, although it is by no means certain that this colony was queenless. The large sitkaensis colonies containing recently adopted suburnbratus queens, however, would seem to support the second or third hypothesis. In regard to this problem in the Euro- pean urnbratus, Donisthorpe (1915) says: "No cases are known of the host queen and the parasite living together in a nest, so unless a female can only be adopted by a queenless colony, it must sometimes happen that a female is accepted by a colony already possessing a queen of its own species. In such a case the intruder must either kill the rightful queen herself, as the female of (non- British) Bothriomyrmex kills the queen of her host Tapinoma or the workers of the host species must themselves assassinate their own queen, as do the workers of Tetrarnorium coespiturn when they have accepted a female Anergates atratzilus." He adds, however, that "Crawley confined several queens of umbrata with queens of nigra and the latter were always killed by the former, which although a little the smaller, is stronger and possesses more powerful mandi- bles." It seems to me that the morphological peculiarities sug- gested by Donisthorpe, namely the much broader and larger head and stronger mandibles so characteristic of the female of all urnbratus forms as compared with the same sex of niger, indicate very clearly that the parasite actually decapitates the host queen in much the same manner as Bothriomyrmex decapitans was seen by Santschi (1906) to decapitate the Tapinoma erraticurn queen and the queen Wheeleriella santschii, the queen of Mono- morium solomonis (Fore1 1906).




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1 74 Psyche [December
2. The fact that one of the sitkaensis colonies observed July 9 contained two fully adopted subumbratus queens and one on the verge of adoption suggests the question as to whether all three queens would survive as mothers of the compound colony or whether two of them would be subsequently eliminated. This question can, of course, be answered only by further investigation. But as the various species of the genus Lasius hitherto observed are decidedly haplometrotic it seems probable that at least in the majority of cases of adoption of several subumbratus queens by a sitkaensis or neoniger colony, the number must be subsequently reduced to unity either by combats among the queens or by the regulatory intervention of the workers.
3. My field observations leave some doubt as to whether sitkaensis or neoniger is the true, or normal host of suburnbratus. Indirect evidence, however, points to the former variety, since the queens and workers of suburnbrutus are much more like the cor- responding phases of sitkahsis in size and coloration and since pure adult colonies of these forms prefer the same shady environ- ment and have the same hypogseic habits. Reiff's Nova Scotia specimens of subumbratus queens from sitkaensis nests may also be cited in this connection. L. neoniger, therefore, would be an unusual or perhaps recently acquired host, and the conditions would be comparable to those of the typical European urnbratus, whose normal host is the typical niger, though it is occasionally parasitic, as Donisthorpe has shown (1915), on the subspecies alienus, the normal host of mixtus.
The rather large number of observed cases of adoption of suhumbratus seems to indicate that the queen of this subspecies is specially favored as compared with the queens of some other temporary social parasites (e. g. Formica rufa and truncicola) by the possession of peculiar myrmecophilous characters (trichomes, exudate organs). I believe that the beautiful golden yellow color and pilosity of the subumbratus queen, which make it resemble the queens of Formica consocians, ciliata, criniventris and oreas, the smaller stature and the delicate odor may be designated as such characters. In this connection I may call attention to the queen of Lasius crinitus, long ago described by Frederick Smith from Cashmir, as being in all probability a temporary social parasite on L. niger or one of its varieties. I have recently seen a few queens



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19171 Wheeler-Social Parasitism of Lusius suburnbratus Viereclc 175 of crinitus from Sikkirn and was struck by their remarkable re- semblance in color and pilosity to the queens of the Colorado F. ciliata. The source of the delicate odor of suburnbratus, of the strong, lemon-verbena odor of our North American Lasii of the subgenus Acanthomyops and of the peculiar pungent, sweetish odor of the Eurasian fuliqinosus, is worthy of further investiga- tion. Meinert and Bonner believe that in urnbratus and fuligi- nosus it comes from the salivary glands. Forel had previously traced it to the head as this portion of the body when crushed emitted a more violent aroma than the thorax and gaster. I have been under the impression that it might originate in the epinotal glands. Since it is so powerful and pervasive that it even sat- urates the walls of the nest a renewed and careful investigation may be required before its precise source in the body of the insect is known.
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1915. Bonner, W. Der temporare soziale Hyperparasitismus von Lasius fuliginosus und seine Beziehungen zu Claviger longi- cornis Mull. Zeitschr. f. wiss. Insekt. Biol. 11, 1915, pp. 14-20.
1909. Crawley, W. C. Queens of Lasius umbratus Nyl., Ac- cepted by Colonies of Lasius niger L.
Ent. Month. Mag.
(2) 20, 1909, pp. 94-99.
1910.
Crawley, W. C. Workers of Lasius flavus (? L. umbratus) among Lasius fuliginosus.
Ent. Rec. 22, 1910, pp. 67-69.
1913. Crawley, W. C. and Donisthorpe, H. St. J. K. The Found- - ing of Colonies of Queen Ants.
Trans. Second Intern. Ent.
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1913. Donisthorpe, H. St. J. K. On Some Remarkable Associa- tions between Ants of Different Species. Rep. Lancast. Ches. Ent. SOC. 36 (1912), 1913, pp. 38-56. 1915. Donisthorpe, H. St. J. K. British Ants, Their Life-History



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176 Psyche [December
and Classification. Plymouth, William Brendon & Son. 1915.
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Donisthorpe, H. St. J. K. and Crawley, W. C. Experi-
ments on the Formation of Colonies of Lasius fuliginosus Females. Trans. Ent. Soc. London, 1912, pp. 664-672. 1908. Emery, C. Remarques sur I'existence de Lasius mixtus dans les fourmili&res de L. fuliginosus. Ann. Soc. Ent. Belg. 52, 1908, pp. 182-183.
1906. Forel, A. Moeurs des Fourmis parasites des Genres Wheel- eria et Bothriomyrmex. Rev. Suisse 2001. 14, 1906, pp. 5 1-69,6 text-figs.
1908. Forel, A. Lettre A la SociM Entomologique de Belgique. Ann. Soc. Ent. Belg. 52,1908, pp. 180-181. 1908.
de Lannoy, F.
Notes sur Ie Lasius niger et le Lasius
fuliginosus. Ann. Soc. Ent. Belg. 52, 1908, pp. 47-53. 1906. Santschi, F. A propos des moeurs parasitiques temporaires des Fourmis du genre Bothriomyrmex. Ann. Soc. Ent. France, 75,1906, pp. 363-392.
1852. Schenck, A. Beschreibung nassauischer Ameisenarten. Jahrb. Ver. Naturk. Nassau, 8,1,1852, pp. 3-149. 1911. Tanquary, M. Experiments on the Adoption of Lasius, Formica and Polyergus Queens by Colonies of Alien Species. Biol. Bull. 20, 1911, pp. 281-308.
1908. Wasmann, E. Weitere Beitrage zum sozialen Parasitis- mus und der Sklaverei bei den Ameisen. Biol. Central. 28, 1908, pp. 257-271,289-306,321-333,353-382,417-441. 1909. Wasmann, E. Ueber gemischte Kolopien von Lasius- Arten.
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On the Founding of Colonies by Queen
Ants, with Special Reference to the Parasitic and Slave- making Species. Bull. Amer. Mus. Nat. Hist. 22, 1906, pp. 33-105, 7 pis.
1910. Wheeler, W. M. The North American Forms of Lasius umbratus Nylander. Psyche, 17, 1910, pp. 235-243. 1917. Wheeler, W. M. The Mountain Ants of Western North America. Proc. Amer. Acad. Sci. 52, 1917, pp. 457-569.



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